The present invention relates to a focused ion beam (hereinafter, referred to as an FIB) machining method and an FIB machining apparatus which are effective in micromachining using a focused ion beam such as cross-sectional machining of micro-devices or new functional materials, preparing of [the] samples for a transmission electron microscope (hereinafter, referred to as TEM), manufacturing of micromachine parts and, more particularly, to an FIB processing method and an FIB processing apparatus which correct a [position] displacement of a beam irradiation position during long-irradiation machining.
An FIB apparatus is disclosed, for example, in Japanese Patent Application Laid-Open No. 9-306402. A method of correcting a machining position is disclosed, for example, in Japanese Patent Application Laid-Open No. 9-274879.
FIG. 12 is a functional block diagram of a conventional FIB machining apparatus. In a vacuum enclosure of the FIB apparatus surrounded by a dashed line, an ion source unit 1 for emitting ions, an ion beam control system 2 for accelerating, focusing and deflecting an ion beam emitted from the ion source unit 1, a sample chamber unit 3 for loading and transporting a sample and a secondary particle detector 6 for detecting secondary electrons and secondary ions emitted from the sample are arranged. The ion beam control system 2 includes a condenser lens, an ion beam control aperture plate, an aligner stigmator, a blanker, a deflector and an objective lens. An ion source control unit 4 and an ion beam control unit 5 are connected to the ion source unit 1 and the ion beam control system 2, respectively. A computer unit 7 is connected to the ion source control unit 4 and the ion beam control unit 5 to control these units together. The computer unit 7 comprises an image control unit 9 for acquiring a scanning ion microscopic (hereinafter, referred to as an SIM) image based on an output signal of a secondary particle detector 6, the image control unit 9 being composed of an image memory and an image processing unit; a CRT 8 for displaying the SIM image; an input operation unit 10 such as a keyboard and a mouse; a mark detecting unit 12; and a machining position correcting unit 11.
In this conventional technology, correction of a displacement of a machining position is performed by the following means during long-time machining within a narrow region which is not required to move its sample stage. Initially, {circle around (1)} a position of a mark for correcting a beam irradiation position selected prior to starting the machining is detected from an SIM image and registered. Then, {circle around (2)} a mark position is detected by acquiring the SIM image of the registered mark at preset intervals during machining, and a position displacement in beam irradiation position is calculated by comparing the detected position with the position of the registered mark to perform correction control of the displacement of the machining position.
In the above-mentioned conventional method, the mark position is repetitively detected by irradiating the FIB and acquiring the SIM image of the registered mark during machining. However, since the mark is eroded by an ion sputtering phenomenon during acquiring the SIM image, the mark is gradually deformed by the damage that occurs when the number of times of detecting the mark is increased. Therefore, there is a disadvantage in that when the mark deformation becomes too large to detect the mark, the displacement of the machining position can not accurately corrected.
The present invention solves such a problem in the conventional technology. An object of the present invention is to provide an FIB machining method and an FIB machining apparatus which can correct a displacement of machining position using a mark for detecting the displacement of machining position even if the mark is damaged by an ion sputtering phenomenon and the shape of the mark is largely changed from the shape of the mark registered prior to starting of the machining.
Further, another object of the present invention is to provide a novel method for automatically detecting termination of an FIB machining.
In order to attain the above objects, in the present invention, when the displacement of machining position in the nth time (where n=1, 2, 3, . . . ) is calculated, SIM image data D[nxe2x88x921] acquired in the time just before the nth time, that is, in the (nxe2x88x921)th time is employed as the reference SIM image data. Then, a position displacement of the image is obtained from matching processing of the two kinds of SIM image data, D[n] and D[nxe2x88x921], to calculate a displacement of machining position.
In the conventional technology, the reference SIM image data is always SIM image data D[0] before starting of machining and is not updated. Therefore, if SIM image data D[n] acquired in the nth time becomes significantly different from the SIM image data D[0] before starting of machining, a large error is produced when matching processing of the two kinds of SIM image data, D[n] and D[0], is performed or, the matching processing can not be performed. In the present invention, since the SIM image data D[nxe2x88x921] acquired in the time just before the nth time is employed as the reference SIM image data to be compared with the SIN image data D[n], a displacement of machining position can be accurately calculated every updating, even if the mark shape becomes significantly different from that in the initial period of the machining so long as an analogy between the two kinds of data of D[n] and D[nxe2x88x921] is maintained.
Although the mark is typically set outside an FIB machining region of a sample, setting of the mark outside an FIB machining region of a sample is not absolutely necessary. It is possible to select a distinctive structure in an SIM image inside an FIB machining region and set it as a mark. In a case of a cross-sectional structure where the selected mark is buried in the sample, the machining can progresse while the machining region is changed so as to trace the mark (structure) by correcting the FIB irradiation position based on the matching processing between the two kinds of SIM image data, D[n] and D[nxe2x88x921].
Further, it is also possible to set a mark in an FIB machining region and use it for detecting a termination of the FIB machining. For example, in a case where the mark is part of a structural body in the sample and a section of the structural body is intended to be formed by FIB machining, the FIB machining is performed while the mark (structural body) appearing in the SIM image is being monitored, and the machining is stopped at the time when the mark disappears from the SIM image or when a preset time after disappearance of the mark has elapsed. Thus, a desired section can be formed.
That is, the present invention is characterized by a focused ion beam machining method of machining a sample using a focused ion beam, the method comprising the steps of acquiring a scanning ion microscopic image of the sample at preset time intervals; calculating a position displacement of the image based on image data D[nxe2x88x921] in a specified region inside a scanning ion microscopic image in the (nxe2x88x921)th time and image data D[n] in the specified region inside a scanning ion microscopic image in the nth time acquired in the above step, where n=1, 2, 3, . . . ; and correcting a machining position by displacing an irradiation position of the focused ion beam by the calculated position displacement.
The scanning ion microscopic image of the sample is displayed on an image display apparatus such as a CRT by scanning on the sample with the focused ion beam and by detecting intensity of secondary particles such as secondary electrons or secondary ions emitted from the sample in synchronism with the scanning.
The specified region for acquiring the image data D[n] inside the scanning ion microscopic image may be a region which is located outside a machined region and includes a distinctive pattern. The distinctive pattern located outside the machined region may be a mark pattern formed prior to starting of machining. Otherwise, the specified region inside the scanning ion microscopic image may be a region located inside a machined region and including a distinctive pattern.
The time interval between acquiring the scanning ion microscopic images may be shortened when the position displacement of the image is larger than a first set value, and the time interval between acquiring the scanning ion microscopic images may be lengthened when the position displacement of the image is smaller than a second set value.
Further, the present invention is characterized by a focused ion beam machining method of machining a sample using a focused ion beam, the method comprising the steps of acquiring a scanning ion microscopic image of a region containing a distinctive pattern located inside a machining region of the sample at preset time intervals; detecting a change in shape of the pattern based on image data D[nxe2x88x921] in a specified region inside a scanning ion microscopic image in the (nxe2x88x921)th time and image data D[n] in the specified region inside a scanning ion microscopic image in the nth time acquired in the above step, where n=1, 2, 3, . . . ; and judging that machining be terminated based on the shape change of the pattern. The shape change of the pattern includes disappearance of the pattern.
A focused ion beam machining apparatus in accordance with the present invention is characterized by a focused ion beam machining apparatus having an ion source, and an ion beam control system for accelerating, focusing and deflecting an ion beam emitted from the ion source, which further comprises a secondary particle detector for detecting secondary particles emitted from a sample by irradiating the ion beam onto the sample; an image control unit for acquiring a scanning ion microscopic image of the sample at preset time intervals based on an output of the secondary particle detector; a matching processing unit for calculating a position displacement of the image from matching processing of image data D[nxe2x88x921] in a specified region inside a scanning ion microscopic image in the (nxe2x88x921)th time and image data D[n] in the specified region inside a scanning ion microscopic image in the nth time, acquired by said image control unit, where n=1, 2, 3, . . . ; and a control unit for controlling the ion beam control system so as to compensate the position displacement of the image calculated by the matching processing unit.
Further, a focused ion beam machining apparatus in accordance with the present invention is characterized by a focused ion beam machining apparatus having an ion source, and an ion beam control system for accelerating, focusing and deflecting an ion beam emitted from the ion source, which further comprises a secondary particle detector for detecting secondary particles emitted from a sample by irradiating the ion beam onto the sample; an image control unit for acquiring a scanning ion microscopic image of the sample at preset time intervals based on an output of the secondary particle detector; and an image comparing unit for comparing image data D[nxe2x88x921] in a specified region inside a scanning ion microscopic image in the (nxe2x88x921)th time and image data D[n] in the specified region inside a scanning ion microscopic image in the nth time acquired by the image control unit, where n=1, 2, 3, . . . , wherein machining is terminated when a predetermined degree of matching between the two kinds of image data compared by the image comparing unit is reached.
According to the present invention, a displacement of machining position during long-time FIB machining can be corrected without involvement of an operator, which contributes to highly accurate machining positions and to semi-automatic machining. In regard to machining of a plurality of machining positions in a plurality of samples, the machining of all of them can be automatically and continuously performed over a several hour period, without involvement by an operator, by pre-registering these machining positions and machining conditions.
In addition, according to the present invention, since a termination of FIB machining can be automatically determined, the FIB machining apparatus can be automatically operated.